var stream = require("stream");
var Readable = stream.Readable;
var rs = new Readable();
var c = 'a'.charCodeAt(0);
rs._read = function(){
    if(c <= 'z'.charCodeAt(0)){
        rs.push(String.fromCharCode(c++));
    }
    else {
        rs.push(null);
    }
}
rs.pipe(process.stdout);